Shift regulator valve



1956 c. J. LUCIA ElAL 7 2,769,350

SHIFT REGULATOR VALVE Filed March 31, 1955 4 Sheets-Sheet 1 I90- I84:542 I88 C RR LL L Tomv 4 2 DE Lonsmv Nov. 6, 1956 c. J. LUCIA ETAL2,769,350

' SHIFT REGULATOR VALVE Filed March 31, 1955 4 Shets-Sheet 5 awe/WMCARROLL J. 0578 JOHN Z. DE (ORE/7N Nov. 6, 1956 c. J. LUCIA ETAL2,769,350

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United States Patent Gfilice Patented Nov. 6, 1956 SHIFT REGULATOR vnrvnCarroll J. Lucia and John Z. De Loreen, Detroit, Mich., assignors toStudebaker-Iackartl Corporation, Detroit, Mich., a corporation ofMichigan Application March 31, 1955, SerinlNo. 498,406

10 Claims. (01.74-472) This invention relates to a control valve for ahydraulic control system, and more particularly it relates to apressureregulating valve in a hydraulic control system for a vehicletransmission which controls the' pressure flow to a hydraulicallyoperated transmission clutch.

In a hydraulic control system for a vehicle'transmission having low andhigh driving ranges and hydraulically operated clutch means to engageone of thedriving ranges, it is frequently a problem to obtain a smoothtransition through the various driving ranges under differentoperatingconditions. For example, under conditions of relatively lowengine speed and high engine torque, when fluid pressure is delivered bythe control system to efiect the disengagement of the low range drive, arelatively high fluid pressure is required to operate the high rangeclutch to prevent it from slipping. However, if full pressureis'admittedto the high range clutch, the'latter is subjected to unduewear during an upshift when the low range drive is not fully disengaged.The high range clutch is also subjected to severe strain during adownshif't when the pressure admitted to the high range clutch isnot'fully vented before the low range drive is engaged.

It is, therefore an object of this invention to provide ashift regulatorvalve which serves a dual function; namely to momentarily retard thefluid pressure flow to the high range clutch during an upshift in orderto allow sufiicient time for the low range driveto be fully disengaged,and also to rapidly vent the high range clutch during downshift.

The applicant has devised a simplified and inexpensively manufacturedvalve which may be conveniently incorporated into :a hydraulictransmission control system of the type described above, and it isdescribed in the following pages in conjunction with a transmissioncontrol system similar to that described in a patent application filedin the names of Forest R. McFarland, Carroll J. Lucia and John Z. DeLorean, Serial No. 498,404, dated March3l, 1955.

Forfurther understanding of the invention reference may be had to theaccompanying drawings in which:

Figures 1 and 2 disclose a schematic view of a hydraulic control systemfor operating valve brakes and clutches for a vehicle transmission;

Figure 3 is an enlarged view in section of the governor regulator valveshown in Figure 2;

Figure'4 is an enlarged sectional view of the throttle valve shown inFigure 2;

Figure 5 is an enlarged sectional view of the throttle limit valve shownin Figure 2;

Figure 6-is an enlarged sectional view of thedir-ect shift throttlevalve shown in Figure 2;

Figure 7' is an enlarged sectional view of the manual selector valveshown in Figure 2;

Figure 8 is an enlarged sectional view-of the reverse shuttle'valveshown in Figure 2.

It is to be understood that the invention is not-limited in itsapplication to the details of construction and arrangernent of'partsillustrated in the accompanying draw- Lu ings, since the invention iscapable of other embodiments and of being practiced or carried out invarious ways. Further, it is to be understood that the terminologyemployed herein is for the purpose of description and not of limitation.

With reference to Figures 1 and 2 disclosing a diaguammatic view of thehydraulic :control system which is similar to that disclosed in theabove referred to McFar land, Lucia and De Lorean application, SerialNo. 498,404, it will be seen that the front and rear pumps Bil-and 220respectively are connected by a fluid pressure gallery 250. The pumpsdraw fluid from a sump and circulate'i-t through the hydraulicallyoperated transi ission controls, as well as the lubrication system ofthe transmission unit.

The front pump is drivingly connected with the engine drive shaft in thecustomary manner and is thus adapted to supply fluid under pressure tothe gallery 250 whenever the vehicle engine is running. The rear pump220*is driven by the output shaft of the engine in the conventionalmanner, and thus operates only when the output shaft is driven. Checkvalves 254 and 256 are disposed at opposite ends of the gallery adjacentthe pump outlet conduits 136a and 220a connecting with the front andrear pumps respectively. The check valves 254 and 256 are arranged sothat as the speedof the car is increased to approximately 5 to 8-milesper hour, the rear pump output increases sufficiently to open the rearpump check valve 256*to admit pressure tothe gallery and thereby closethe front pump check valve 254. When the front pump is operating, thefront pump output pressure is delivered from its outlet to a pumpregulator valve I, through the connecting conduit 258i The pumpregulator valve I includes a valve 260' which is reciprocally-mountedwithin a housing 262; The valve ass has four lands 26th:, 260b, 26%,260d; the first three all being of equal diameter but smaller than thediameter of'land 269d. The valve 260 is urged to the left by a spring266 retained between the right hand end of the valve and the adjacenthousing wall. The action of spring 266' is supplemented by a torqueresponsive throttle limit valve pressure admitted to the right handend'of housing 262 through conduit 268, and which exerts a force againstthe right side of valve land 260d. Gallery fiuid pressure is deliveredthrough conduit 270 to the left hand end of the housing and urges thevalve 260 to the right against the action of the spring 266 and thethrottle limit pressure. In addition, the movement of valve 260 to theright is assisted by the modulating valve fluid pressure delivered tothe housing through conduit 272, which exerts a force against the leftside of land 2'6@d.' Restricted orifices 268a and 272a are connected inseries with conduits 268 and 272, respectively, to minimize the effectof surging of the fluid pressure therein on the valve operation.

When the front pump is operating and the gallery pressure exceeds apredetermined limit, the valve 260 is moved a suihcient distance to theright so that land 2605 uncovers conduit 274 connecting with the intake275 of the front pump 130, and fluid pressure from the conduit 258' ispermitted to flow therethrough back to the front pump.

Gallery fluid pressure is also delivered to the pump regulator valve Ithrough conduit 276, and under normal operating conditions is permittedto flow between lands 26Gb and 2360c into conduit 2'78 which connectswith the converter valve J. In the event the rear pump'220 builds upexcessive gallery pressures, valve 260 is moved to its extremeright-hand position, and as a result, land 260C uncovers vent line 280connecting with the sump 252,-and the gallery pressure from conduit 276is vented therethrough.

From the above description it Will be appreciated that the pumpregulator valve 1 controls the pressure of the gallery fluid, and alsodetermines which of the two pumps, independently or in combination, areto be operatively connected to the control system. In addition, if thereis a large demand of fluid pressure while the rear pump 220 isoperating, the regulator valve will operatively connect the front pump13!) with the system. Also, it will be seen that the applicantsregulator valve and gallery arrangement insures that sufficient pressureis first delivered to the gallery to operate the transmission clutchesand brakes, before pressure is admitted to the converter valve J.

The converter valve I serves the dual function of maintaining thedesired high fluid pressure in the converter A when the lock-up clutch Bis inoperative and the converter is rendered operative, and a fixedpercentage lower fluid pressure in the converter when the converterlockup clutch B is engaged. The converter valve includes a valve 290with two lands 220a and 29Gb of equal diameter, and an elongated valvestem 292 which extends into a separately enclosed fluid pressure chamber294 housing valve 296. A spring 298 interposed between a spring stopmember 304) and the right hand end of valve 296, tends to hold the leftside of valve 296 in contact with the right hand end of valve 290. Whenthe direct shift valve K is opened the pressure of the fluid in chamber294 moves the valve 296 to the right, against the action of spring 298.Also, the fluid pressure from conduit 302 exerts a force against the endof the valve stem 292, thereby tending to move valve 290 to the left,but with less force than when the spring 398 forces the valve 296against stem 292 of valve 2%. When the direct shift valve K is closedand no fluid pressure is delivered through conduit 302, valve 2% bearsagainst valve stem 292, and spring 298 moves both valves 2% and 290 tothe left.

As valve 290 is moved to the left, land 29% uncovers conduit 278connecting with the pump regulator valve 1, and fluid pressure isadmitted between lands 290a and 29017, through conduit 394 to theconverter A, and thence through a restricted orifice 310 in theconverter outlet conduit 312 connecting with a cooler 314, which in turnconnects with the sump. The fluid pressure contained in line 304 is alsoconducted to the left hand end of the valve 290 through connectingconduit 306, which tends to move the valve 290 to the right against theaction of spring 298, thereby effecting a reduction in the fluidpressure delivered to the converter as land 299a meters the flow throughconduit 278.

When gallery pressure is delivered to chamber 294 through conduit 302,the force exerted thereby against the right end of valve stem 292, whichis of smaller diameter than valve 296, permits valve 290 to move to theright so that land 230a meters a reduced pressure through conduit 278 tothe converter A. By this arrangement a fixed percentage of lower fluidpressure is admitted to the converter for lubrication and coolingpurposes when the latter is inoperative and the converter lock-up clutchis engaged. Therefore, it will be seen that in the applicants controlsystem arrangement, the operative converter lockup clutch pressure andthe converter pressure are self compensating in the event of pressureleakage in the lockup clutch, when the latter is engaged. If thepressure delivered to the converter exceeds a predetermined limit, valve290 is moved a sufiicient distance to the right so that land 290a coversconduit 278 and land 290 uncovers vent line 308, with the result thatthe pressure in conduit 304 is vented to the sump. Thereafter, spring298 and the gallery fluid pressure if :any, returns valve 290 to itsnormal metering position.

It will be appreciated that the desired percentage differential in fluidpressure delivered to the converter when the latter is activated orrendered inoperative, may be obtained by varying the differentials inthe diameters of the valve stem 292 and valve 296. In addition, themaximum fluid pressure delivered to the converter through the conduit304 may be controlled by varying the tension of spring 298.

A speed responsive fluid pressure as determined by the speed of theoutput shaft 139 delivered by the governor valve H is utilized inconjunction with the torque responsive fluid pressure as determined bythe position of the accelerator pedal delivered by the throttle valve Lto operate the various controls in the hydraulic system, which in turnoperate the transmission brakes and clutches, in a manner subsequentlyto be described.

With specific reference to Figure 3, it will be seen that the governorvalve H includes a lightweight high speed valve 320 and a heavierweighted low speed valve 322 which are reciprocably mounted in valvechambers 324 and 325, respectively. The valve chambers 324 and 326 arefixedly mounted on output shaft 139, and the centrifugal force generatedby their rotation tends to move the valves 32% and 322 away from and atright angles to the axis of the shaft. The centrifugal force acting uponthe high speed valve 32% is supplemented by a spring 328 retained withinthe housing 324 between the under side of the valve and a spring stopmember 330 Which bears against the output shaft.

Fluid pressure from the outlet conduit 220a of the rear pump 220 isdelivered to the high speed valve chamber 324 through conduit 332. Thespring 328 normally positions the valve 32% so that land 326a uncoversconduit 332, and thus the rear pump pressure is permitted to flow out ofthe valve chamber through conduit 334 to the low speed governor valvechamber 326. Pressure from conduit 334 is also delivered to the upperend of the high speed valve chamber 324 through connecting conduit 336,and tends to move valve 320 inwardly against the action of the spring328 and the centrifugal force, if any. As a result, the flow of fluidpressure from conduit 332 is metered by the relative movement of valveland 320a in respect thereto. If the pressure in conduit 334 exceeds apredetermined maximum limit for any driving speed, valve 320 is movedinwardly a suflicient distance by the fluid pressure at its outer end sothat land 320a covers conduit 332 and land 32% uncovers vent port 338,Whereupon, fluid pressure from line 334 flows through vent port 333communicating with the sump.

It will be appreciated that the fluid pressure in conduit 334 at leastmust be equal to the force exerted by spring 328 before the high speedvalve 32:) commences to regulate the governor output pressure. It willalso be appreciated that the relatively light weight high speed governorvalve is adapted to provide a more sensitive pressure regulation at highvehicle speeds than would be possible using only a heavier weighted lowspeed valve, next to be described.

The low speed valve 322 'has three lands; lands 322a and 32212, whichare disposed near its outer end and center portion, respectively, beingof equal but smaller diameter than land 322a disposed adjacent theoutput shaft 139. When the output shaft 139 is rotated, valve 322 ismoved outwardly by centrifugal force and land 322k uncovers conduit 334whereupon fluid pressure is permitted to flow between lands 32211 and3220 to the governor outlet conduit 340. At the same time, the fluidpressure in chamber 326 tends to move valve 322 inwardly, due to thelarger diameter of land 3220, and as a result, land 322b meters thepressure flow from conduit 334. It will be appreciated that the lowspeed valve 322 is adapted to provide a relatively steep increase ingovernor output pressure, due to its heavier weight and the differentialarea of lands 32211 and 322C.

If the pressure in conduit 340 exceeds a predetermined limit, valve 322is moved inwardly a suflicient distance so that land 3221) coversconduit 334. Land 322b also uncovers a port 342 communicating with theoutlet conduit 340 through connecting conduit 344. Thus, fluidpresspectively, is reciprocably mounted within the housing 360. Thepiston.370 has a radial vent port 372 near its left hand end, and aradial pressure port 374 near its center. A throttle idle spring 376disposed about the left end of piston 370, is loosely retained betweenthe left side of land 370a and the adjacent housing end wall 378. Itwill be noted that spring 376 acts to move the piston 370 to the right,only when the piston is moved suificiently to the left that spring 376bears against the housing wall 378. The piston 370 is urged to the leftby spring 380 disposed at its opposite end. The spring 380 is retainedbetween the right hand housing end wall 382 and a cylindrically shapedspring retainer 384, which fits about the right end of piston 370 andabuts land 37017.

A valve 390 having lands 390a, 390b, and 3900, is slidably mountedwithin the piston 370, in axial alignment therewith. A plunger 392 ismounted for reciprocal movement through an opening 394 in the housingend wall'382 and extends through the cylindrical spring retainer 384.The left end of the plunger 392 is received within the piston 370 and isconnected to the right end of valve 390 by a ball and socket coupling396. The opposite end of the plunger 392 is connected by suitablelinkage 397 to an engine accelerator pedal 398, as showndiagrammatically in Figure 2a. Thus, the position of the plunger 392 andvalve 390 relative to the piston 37 0, is dependent upon the enginethrottle setting. The leftward movement of the piston 370 and valve 390towards the full closed throttle position is limited by an adjustablestop member 399.

When the plunger 392 and valve 390 are'moved toward the full closedthrottle position, spring 380 moves piston 370 sufficiently to the leftso that the throttle idle spring 376 bears against thehousing wall 378.As a result, piston 370 is positioned so that the right hand land 37%closes the outlet port 364 and, the left hand land 390a of valve 390partially opens the piston vent port 372, and land 1590b opens port 374.Under these conditions, thegallery pressure from conduit 368 ispermitted to flow into a passageway 408 formed between piston 370 andvalve 390. A portion of the fluid pressure in passageway 400 flowsthrough vent port 372 to the sump, and the remainder flows through port402 in the piston, and thence to the housing outlet port 362. Thepressure delivered to the outlet port 362 exerts a force against theleft side of land 37 a urging the piston to the right, and port 374-isthereby partially closed by valve land 390b.

When the valve 390 is moved, a relatively small distance toward the openthrottle position, spring 376 no longer bears against the housing wall378, and thus the fluid pressure at the outlet port 362 alone acts tomove the piston 370 to the right against the action of spring 380. As aresult, a reduced pressure flow is metered through port 374. It will beappreciated that throttle valve outlet pressure remains approximately indirect proportion to the speed increasing position of theacceleratorpedal, andis therefore substantially proportional to thetorque output of the engine. In this connection, it will be seen thatthrottle idle spring 376 is utilized to position-the piston 370 such asto provide a rapid increase in the throttle valve pressure as the enginethrottle is initially opened and a .corresponding rapid increase inengine torque is developed. A high throttle pressure is required underthese operating conditions to ensure the positive -engageinent ofthe-transmission brakes and clutches.

When the valve and :plungerare moved beyond the full throttle setting tothe'kickdown position, valve land 390a closes vent port 372, and thefull gallery-pressure delivered to the outlet ,port 362, moves thepiston 370 to its extreme right hand position against stop'404. As.airesult, land.370b uncovers outlet port 364, and gallery pressureflows .therethrough, into conduit 406 connecting with the low-highshiftvalve N.

Inthe event the driver quickly removes his foot from the acceleratorpedal and the valve 390 ,-is moved rapidly to the-left, valve land 390ais moved momentarily beyond the-piston, uncovering vent port 372. Thus,spring 380, unopposed by the gallery fluid pressure, rapidly returnspiston 370 towards the closed throttle position.

The throttle limit valve 0 :as shown in Figure .5, ,in-

cludes a valve 420 with lands 420w and 4201) disposed near its oppositeends, which is mounted for reciprocal movementwithin a cylindricalhousing 422. A spring 424 :retained between the left hand end of thevalve 420 and the adjacent'housing end wall, tends to move the valve tothe right, towards a valve stop member 426. When valve 420 bears againststop 426, an :inlet port 428 communicating with a throttle valvepressure conduit 430 is uncovered bythe right hand land 420i). Thethrottle valve pressure. is then permitted to flowaround the valve to anoutlet port 432 .which.is connected with the low regulator valve'R byconduit 434. Also, as previously described, fluid pressure .is deliveredto the right hand end of the pump regulator valve I, through connectingconduit 268.

In addition, pressure from conduit 434 is delivered by branch conduit434a to .a port 436 at the right hand end of housing 422, which urgesvalve 420 to the left against the action of spring 424 and land 420!)thereby meters the pressure flow through the actionof spring 424 andgrooved portion of valve 420 thereby meters the pressure flowthrough-the inlet port 428.

It will be appreciated that the maximum pressure which is permitted toflow through the throttle'limit valve 0 cannot exceed the force exertedby spring 424, and the maximum outlet pressure maybe determined byvarying the tension of the spring. In theevent of a sudden surge ofpressure in conduit 434 and branchconduit 434a, valve h 420 is moved tothe left a sufficient distance so that its left handland 420a uncoversvent port 438 connecting with the sump, and the right hand 'land 42%covers inlet port 428. When the excessive fluid pressure in line 434 hasbeen vented through port 438, spring 424 returns valve 420 to its normalmetering position.

The direct shift throttle .valve Q, as shown in Figure 6, includes acylindrical chamber or housing 440 With valve stop members 442 and 444disposed at opposite ends thereof. The housing 440 has a radiallyextending pressure inlet port 446 formed at its left hand end connectingwith a throttle valve pressure conduit 448 which in turn connects withthe throttle valve outlet port 362. Another radial inlet pressure port450 is disposed in the side of the valve housing near its center whichis connected by branch line 448a with conduit 448. An outlet'pressureport 452 also formed in the side of the valve housing near its center,connects with conduit 454 communicating with the direct shift valve K.

A valve 456 having land 456a and 456!) formed in its left hand endand'near itscenter, respectively, is reciprocably mounted within thechamber 440. A spring 458 retained'between the right hand end of thevalve 456 and the adjacent housing end wall, urges the valve 456 towardsthe stop member 442.

As the throttle pressure enters the valve chamber through inlet port446, the valve 456 is moved to ,the right against the force exerted bythe spring 458, and

the outletport .452 and into conduit 45.4. The fluid pressure in conduit454 is delivered to the right side of land 456b by a branch conduit 454aconnecting with a radial port 460 near the right end of the housing. Thepressure in conduit 454 and 454a, therefore, assists spring 458 to movethe valve 456 to the left, and land 456b meters the pressure flowthrough inlet port 450. If a surge of pressure occurs in line 454 thevalve is moved momentarily to the left against stop 442, and land 45Gbcloses the inlet port 450 and land 456a uncovers vent port 462. Theexcess pressure in line 454 is then vented through the vent port 462 tothe sump until the valve is returned to its normal metering position.

From the above description, it will be apparent that the purpose of thedirect shift throttle valve Q is to deliver a pressure which is apredetermined fixed amount less than the throttle valve pressure andthis differential in pressure is determined by the tension of spring458. If for example, spring 458 has an applied force equivalent to 35pounds per square inch, the throttle valve pressure delivered throughconduit 448 must equal approximately 35 pounds per square inch beforethe valve is opened and fluid pressure is permitted to flow into conduit454. Thereafter, the pressure in conduit 454 remains approximately 35lbs. less than the throttle valve pressure as the latter is increased.

As will be seen in Figures 2 and 2a, conduit 454 from the direct shiftthrottle valve Q, communicates with the right hand portion of acylindrical housing 480 of the direct shift valve K. The governorpressure conduit 340 connects with the left hand end of the housing 480,and conduits 482 and 484 communicate with the interior of its centerportion. Conduit 482 is connected with the converter lock-up clutch B,and conduit 484 connects with both the manual selector valve U and thelow-high shift valve N.

A valve 486 is mounted for reciprocal movement Within housing 480 and isnormally held in engagement with the left hand housing end wall by aspring 488 retained between the right hand end of the valve 486 and theadjacent housing end wall. The valve has five lands; lands 486a and4861; near its left hand end being of equal diameter, and lands 4860,486d, 486e near its center and right hand end, respectively, being ofequal diameter and larger diameter than lands 486a and 486b. For thereasons of economy and convenience of manufacturing, the valve 486 maybe formed by two or more separate valves disposed in axial alignment.

When the engine is idling, spring 488 is assisted in moving Valve 486 tothe left by the direct shift throttle pressure from conduit 454 (a fixedamount less than the throttle pressure with a minimum of 35 p. s. i.).The direct shift throttle pressure is admitted into the interior of anaxial bore 4% in the right end of the valve through a connecting radialbore 492, and reacts against the right side of valve land 486a With thevalve in its left hand position, land 486d covers conduit 484communicating with the low-high shift valve N, and conduit 482connecting with the converter lock-up clutch B is vented to the sumpthrough vent port 494 which is uncovered by land 4860. When the governorpressure has increased sufficiently to move valve 486 to its right handposition within housing 480, land 4860 covers vent port 494 and land486d uncovers conduit 484. Thus, the low-high shift valve pressure fromconduit 484 is permitted to flow between lands 4860 and 486d to conduit482, and thence to pressure chamber 100 in the converter lock-up clutchB. In addition, pressure from conduit 482 flows through branch line 382to the converter valve I, which as previously explained meters a reducedpressure flow to the converter A while the lock-up clutch B is engaged.

When the vehicle speed is decreased, and the governor pressure iscorrespondingly decreased, the throttle pressure and spring 488 move thevalve 486 to its left hand position, and the pressure in the lock-upclutch conduit 8 482 is vented to the sump. From the above descriptionit will be apparent, that the direct shift valve K serves to control theengagement of the converter lock-up clutch B when the vehicle hasattained a predetermined driving speed.

The following paragraphs include a description of the low high shiftvalve N, the low regulator valve R, the shift regulator valve S and themodulating valve T, and a detailed explanation of their interrelatedoperation.

The low high shift valve N includes a cylindrical housing 588 the righthand end of which connects with a branch conduit 340a of the governorpressure conduit 340. The kick-down throttle valve pressure conduit 406connects with housing 580 near its right hand end, the direct shiftvalve conduit 484 and a conduit 502 communicating with the gallery 250are both connected with the middle portion of the housing. Also, aconduit 504 is connected near its left hand end, which communicates withthe outlet port 362 of the throttle valve L. A bypass line 506 connectswith the left hand end and center portion of the housing interior onopposite sides of conduit 504. In addition, the housing 500 has a radialvent port 508 near its center, and vent ports 510 and 512 disposed nearits right hand end between conduits 484 and 406.

A piston 514 having an axial bore 516 in its left hand end, isreciprocally mounted within the left hand end of the housing 50f). Thepiston 514 has lands 514a, 514b and 5140 at its left end, center andright end, respectively; lands 514a and 5141) being of equal andslightly larger diameter than land 5140. A spring 518 seated within thepiston bore 516 and retained against the left hand housing end wall508a, urges the piston 514 to the right.

A valve 520 is reciprocabiy mounted in the right hand end of the housing500, and is disposed in axial alignment with piston 514. The valve 528has a land 520a at its left hand end and a land 5281) of larger diameterat its right hand end. Governor pressure delivered to the right end ofthe housing 560 exerts a force against the right side of land 528b,thereby moving valve 520 to the left, into engagement with the right endof piston 514.

As shown in Figures 2 and 2a, when the engine is idling and the manualselector valve U is placed in its neutral position, the piston 514 andvalve 520 are moved by spring 518 to the right against the right handhousing end Wall 5001). Under these conditions, piston land 514auncovers throttle pressure conduit 504 and covers the right end of theby-pass conduit 586. The throttle pres sure from conduit 584 upon beingadmitted to bore 516, assists the spring 518 in maintaining the pistonin its right hand position so that land 5141) covers the gallerypressure conduit 582, and vent ports 508, 510 and 512 are opened. As aresult, no pressure can flow through conduit 484 to the direct shiftvalve K and the manual selector valve U, and for reasons that willsubsequently be described, neither the low brake D or the high clutch Eare engaged.

When the vehicle commences to move, and the governor pressure in branchconduit 340a is proportionally increased, the valve 520 and piston 514are at first slowly moved toward the left. Thus, piston land 514bpartially uncovers conduit 502, and fluid pressure is permitted to flowbetween lands 51412 and 514s into conduit 484. It will be apparent thata metering action momentarily occurs between land 514k and conduit 502when a balance is attained between the governor pressure at the rightside, and the spring and and throttle pressure on the left side, of thevalve. It will also be noted that when the low high shift valve N closesgallery conduit 502, no pressure can flow to the converter lock-upclutch B through conduit 482 regardless of the position of the directshift valve K. A more complete description of the combined operation ofthe direct shift and the low-high shift valves will subsequently begiven.

As the governor pressure increases, the piston .514 is moved further tothe left, and land 514a covers the throttle pressure conduit 50d, .andthe fluid pressure in bore 51-6 is vented through by-pass line 506 tovent port 508.connecting with the sump. As a result, the piston is movedrapidly to its extreme left hand position against the left hand housingend wall 500a since spring 518, alone, opposes its movement in thisdirection. Full gallery pressure is then permitted to flow throughconduit 484, and the high range clutch E is engaged depending upon .theposition of the manual selector valve, which will subsequently bedescribed in detail. In this connection, the governor pressure isassisted in holding the piston 514 in its extreme left hand position, bythe force of the gallery pressure reacting against the right side ofland 514b; the latter being of larger diameter than land 5140.

In the event the kick down throttle pressure is admitted to conduit 406by the throttle valve L (when the accelerator pedal is depressed beyondits full throttle position), this pressure reacts against the left sideof land 52% of valve 520, and the latter is moved to the right, if thegovernor pressure does not then exceed a predetermined limit.Consequently, the spring 518, then being unopposed by the governorpressure, moves the piston 516 rapidly to the right. The gallerypressure conduit 502 is then covered by land 514b, and no fluid pressurecan flow through conduit 484 to the direct shift valve K. Therefore,regardless of the position of the latter, no pressure can be deliveredthrough conduit 432 to engage the converter lock-up clutch B andconsequently the converter A is activated. Also, since no pressure isdelivered through conduit 484 to the manual selector valve U (and thenceto the high range clutch and the release side of the low range brake D),the high range clutch may .be inactivated and the low range brakeengaged depending upon the position of the manual selector valve. Adetailed description of the kickdown operation will be given followingthe description of the manual selector valve and its interrelatedoperation.

When the vehicle speed decreases, and a corresponding lower governorpressure is delivered to the right side of the valve, the piston 514 isat first moved slowly to the right by the action of the spring 518,thereby reducing the pressure flow to conduit 434. As the governorpressure decreases further, the piston is moved sufficiently towards theright that land 514a uncovers the throttle pressure conduit. Fluidpressure is then admitted to the piston bore 516 and the piston israpidly moved thereby, to its extreme right-hand position, in engagementwith the right hand housing end wall 50Gb.

It will be apparent upon reading the subsequent paragraphs, the lagpreceding a positive, rapid movement of the piston 514, ensures that theoperative transmission brake or clutch is released before the other isengaged.

'The fluid pressure admitted to conduit 484 by the lowhigh shift valve Nis conducted to the manual shift valve U. From there it flows throughconduit 534 to the upper side of piston 535 in the low range brake D toeffect its release. A restricted orifice 536 is connected in series withconduit 534 and serves to retard the fluid pressure flow to the releaseside of the low range brake D, for reasons subsequently to be described.The fluid pressure in conduit 534 is also conducted to the low regulatorvalve R and the shift regulator valve S, by branch conduits 538 and 540,respectively. Pressure flows from the shift regulator valve S throughconduit 542 to the piston chamber 188 .in the high range clutch E,thereby effecting the engagement .of the high range planetarygearsystem.

Thelow regulator valve R has a cylindrical shaped housing- ;544 with twoclosely spaced radial ports 546 and 1548 in its side. A valve 550 havinglands SSOaand 55% near its left hand end and center portion,respectively, is reciprocably mounted within the housing. The valve 550is urged to the left by a spring 552, which is loosely disposed aboutits right hand end and retained between the right side of land 5501) andthe right hand ho sing end wall. Throttle limit valve pressure isdelivered by conduit 434 to the left hand end of housing 544, and exertsa force against the left side of land 550a, thereby tending to move thevalve to the right against the action of spring 552.

A fluid passageway 554 extends through the middle portion of valve 550at an oblique angle to its longitudinal axis. When the valve is moved tothe right into engagcment with right end of the housing 544, the.opposite ends of passageway 554 communicate with ports 546 and 548,respectively. The tension of spring 552, is such that when the pressuredelivered to the left hand .end of valve 559 is approximately 10% of themaximum throttle limit pressure, the valve is moved to its right handposition. Under these conditions, the fluid pressure inconduit 534 mayby-pass orifice 536, by flowing through branch conduit 538 and valvepassageway 554 to port 543, and thence through conduit 556 whichconnects with conduit 534 at a point between the low range brake D andthe orifice 536.

Thus, it will be apparent that above 10% of the maximum throttle limitpressure, orifice 536 is by-passed, and the full pressure in .conduit534 is utilized to effect the rapid engagement or release of the lowrange brake D. When less than 10% of the maximum throttlelirnit pressureis developed, the low regulator valve R is closed and the pressure flowthrough conduit 534 is retarded by orifice 536, and consequently, theengagement or release of the low range brake D is momentarily delayed.It will be appreciated that under conditions of low throttle pressure,and a corresponding low engine torque, the slower release of the lowbrake will result in a smooth transition from the low to the high rangethrough the planetary gear system. At higher engine torque, however, asimilar delay in the release of the low brake, would result in thepremature failure of the high range clutch.

As shown in Figure 2, the shift regulator valve S includes a cylindricalhousing 558 having radially disposed pressure inlet ports 560 and 562near its center which connect with the by-pass lines 538 and branchconduit 540, respectively. The high clutch pressure conduit 542 isconnected near the left hand end of the housing 558, and a branchconduit 564 connecting therewith, delivers fluid pressure to the leftend of the housing interior. It will be noted that the pressure suppliedthrough branch conduit 540 is momentarily of lower pressure than thatdelivered through conduit 538, because the latter bypasses therestricted orifice 536.

A piston 568 having lands 568a and 56812 near its opposite ends isreciprocably mounted within the left hand end of housing 558. The piston568 has radial ports 574 in its side which communicate with an axialbore 576 extending inwardly from the left end of thepiston. A valve 580with lands 580a and 58015 near its left end and center portion,respectively, is reciprocably mounted in the right end of the housing558 in axial alignment with the piston. A spring 582 is loosely disposedabout the right end of valve 580 and is retained between the left sideof land 58Gb and the adjacent housing end wall. The spring 582 urges thevalve and piston 558 towards the left end of the housing,

When the piston is in its left hand position, pressure from the by-passconduit 538 flows freely around the valve (between lands 568a and 5681;)into conduit .542. At the same time, the outlet pressure in conduit 542is delivered to the left side of piston land 568a by branch conduit 564,and the piston thereby is moved slowly towards the right, first againstthe action of spring 582, and thereafter against the opposing forceexerted by the pressure admitted through conduit 540. As the piston ismoved to the right, fluid pressure from conduit 542 fills 1 1 bore 576.The entire end surface of piston 568 is then exposed to the force of thefluid pressure, and therefore, the piston 568 is moved further to theright so that land 568a partially covers conduit 542, reducing thepressure flow in conduits 542 and 564 until a balance is substantiallyattained between the latter and the spring 582.

The fluid pressure delivered to the regulator valve 5 through conduit540 initially has no eifect on the position of piston 568 because of theaction of the spring 5'82. When this pressure increases to a point whereit exerts a greater force against the piston and valve than spring 582,valve 580 is moved thereby to the right against the housing wall. Also,the pressure from conduit 54-4 reacts against the right side of piston568, moving the latter to the left until a balance is reached with theincreased regulator valve outlet pressure in conduits 542 and 564. If,in the event, the pressure in conduit 542 decreases due to a leak in thehigh range clutch E, for example, the piston 568 is moved to the left,thereby permitting full gallery pressure from conduit 538, to flowbetween lands 568a and 568b.

From the above description it will be seen that the shift regulatorvalve S controls the pressure flow to the high range clutch E andassists in maintaining a predetermined high pressure in conduit 542while the clutch E is engaged. During a shift from the low to the highrange through the planetary system, for example the regulator valve Sfirst acts to admit an increasing gallery pressure into conduit 542 (asthe pump output increases), then momentarily the pressure increase isretarded (even though the vehicle speed and gallery pressure areincreasing), and thereafter the pressure in conduit 542 is permitted toincrease until it reaches the maximum gallery pressure. This delay inthe rate of pressure increase in conduit '542 allows sufiicient time forthe low range brake D to be fully released before the high range clutchE is engaged.

During a downshift, pressure in conduits 540 and 534 is vented throughvent port 510 in the low high shift valve N. As the piston 568 is movedto the right the radial piston ports 574 are aligned with a vent port586, and the pressure in conduit 542 and piston bore 576 is abruptlyvented therethrough. When the pressure in conduit 542 is reduced to apoint where it produces a force approximately equal to that of spring582, the piston is moved to the left by the spring, and the remainder ofthe pressure in conduit 542 flows through conduits 538, 534, and 484 tovent port 510 in the loW high shift valve N. The rapid venting action ofthe shift regulator valve S during a down-shift, ensures that the highrange clutch E is fully released before the low brake D is engaged,thereby providing a smooth transition between the planetary gear rangesand preventing the early failure of the high range clutch.

As shown in Figure 2a, the modulating valve T has a housing 610 with aninlet port 612 connected with the governor pressure conduit 340. Thehousing also has radial ports 614 and 616 in its side connecting withthe pump valve conduit 272 and a branch conduit 484a of the low-highshift valve conduit 484, respectively. The left hand end of the housingis connected with conduit 534 through a branch conduit 534a.

A valve 620 having lands 620a and 62Gb near its opposite ends, isreciprocably mounted within the housing 610, and is normally urgedagainst the left hand end thereof by a spring 622. The spring 622 isretained between the right end of the valve and a stop member 624 whichis fixedly mounted at the right end of the housing. When the valve ismoved to the left, land 620a opens port 612 and land 6201; closes port616. Fluid pressure is then permitted to flow from the governor pressureconduit 340 around the valve, and into conduit 272 connecting with thepump regulator valve I. As previously explained, under these conditions,the pump regulator valve I acts to reduce the gallery pressure inaccordance with the speed of the vehicle.

When the low-high shift valve N admits fluid pressure to conduits 484,534 and 542 to activate the high range clutch E, pressure from line 534aexerts a force against the left side of the modulating valve, and thelatter is urged towards the right against the action of spring 622. Land629a then covers the inlet port 612, and land 62% opens port 616,whereupon pressure flows from conduit 484a to conduit 272. As previouslydescribed, the pressure delivered through conduit 272 assists in movingthe pump regulator valve 260 to the right and the front pump pressurethereby is reduced. If the high range clutch E is operative and thepressure in conduit 484a is below a predetermined limit theproportionately reduced pressure admitted to conduit 272 is notsuflicient to move the pump regulator valve 260 to the right. Thus, thegallery pressure is permitted to increase, thereby ensuring the highrange clutch E of adequate pressure to remain fully engaged. It will benoted that this latter condition (of relatively low pressure in conduit484) is most likely to occur when the engine torque is high and vehiclespeed is low, as for example, when starting in high range converter, andit is under these circumstances, that maximum gallery pressure isrequired to prevent the high range clutch from slipping.

It will be appreciated that another outstanding feature of theapplicants pump regulator valve I is that in combination with the closedfluid circuits connecting the various control valves and transmissionclutch and brakes with the reservoir, it acts to compensate for loss ofpressure due to leakage in the high range clutch under conditiOns ofhigh engine torque. In this respect, it will be seen that if a leakshould occur in or near the high range clutch, the resulting loss ofpressure in lines 542, 534 and 534a will effect the movement of themodulating valve 620 to the left due to the action of the spring 622. Asa result under conditions of high engine torque normally developed atlow engine speeds, a proportionally lower governor pressure is admittedfrom conduit 340 and conduit 272 to the regulator valve I, near the leftside of the valve land 2664!. As a result, the then relatively highthrottle limit pressure delivered through conduit 268 and the force ofspring 266 tends to move the regulator valve 269 to the left, overcomingthe governor pressure which is exerting a force in the oppositedirection. As previously explained, movement of the regulator valve tothe left causes valve land 2601? to cover conduit 274 with the resultthat the pressure in the gallery 250 is increased.

With particular reference to Figure 7, it will be seen that the manualselector valve U has a cylindrical housing 660 with radially disposedports 662, 664, 666, 668 670, 672 and 674 along its side. Ports 662 and666 communicate with the hi h clutch pressure conduit 534 and a branchconduit 534a connecting therewith, respectively, and port 664communicates with a high-low shift valve pressure line 484. Ports 668and 670 connect with the low brake pressure conduit 532 and a branchconduit 532a thereof, and port 672 communicates With the gallery 25%through conduit 676. Port 674 connects with conduit 678 which in turncommunicates through branch conduits 678a and 678b with the reverseshuttle valve V and the operative side of piston 679 of the reversebrake F, respectively.

A valve 680 having lands 680a, 680b, 6800, and 680d is mounted forreciprocable movement within the housing 660, and its right hand end isconnected to a lever 682 by a pin 684, which in turn may be secured bysuitable linkage (not shown) to a conventional manual gear shift lever.By selectively positioning the gear shift lever, the driver may movevalve 680 to one of five positions, indicated generally at 686; namely Idesignating the neutral or park position, indicating the normal drivingrange, D for rapid acceleration, L for low gear drive, and R forreverse.

A series of five detents 688 are formed along the left hand end of valve680 which corresponds to the five manually selectable positionsindicated above. Two spring biased ball elements 690 and 692 are mountedfor reciprocable movement at right angles to the longitudinal axis ofvalve 680, and are adapted to engage one of the five detents 688 therebyholding the valve 680 in one of its five manually selectable positions.The ball elements 690 and 692 are housed within radially disposedcylinder chambers 694 and 696, respectively, which are secured to theside of the housing 660, near its left hand end. The elements 690 and692 are urged into engagement with the valve detents 688 by springs 698and 700 retained between the elements and the outer housing end walls702 and 704, respectively. Fluid pressure from the governor conduit 340is introduced through branch conduits 34012 and 340s to each of thechambers 694 and 696, respectively. Thus, when the vehicle is driven,and the governor pressure is increased accordingly, the ball elements690 and 692 are held firmly in engagement with the detents 688. Theselector valve 680 is thereby held in position and cannot beaccidentally moved while driv- A radial bore 706 near the right end ofthe selector valve 680 is disposed so that it is aligned with conduit678 only when the selector valve is placed in the L position. The radialbore 706 connects with an axial bore 708, which in turn communicatesthrough suitable means (not shown) with the sump. Conduit 678communicates with the recessed portion of the right end of valve 680 inthe P, and D positions of valve U which permits the reverse brake F tobe vented to the sump through suitable means (not shown).

The reverse shuttle valve V, shown in Figure 8, includes a cylindricalhousing 710 disposed in axial alignment with the longitudinal axis ofthe modulating valve housing 610, and is separated therefrom by the stopmember 624. It will be appreciated that the two housings may be formedseparately if desired. Housing 710 has radial ports 712 and 714 formednear its opposite ends which connect with branch conduit 678a from themanual selector valve U, and conduit 716 communicating with theinoperative side of piston 679 of the reverse brake F. A branch conduit676a connects the gallery pressure conduit 676 with a third radial port718 formed near the middle of housing 710.

A valve 720 having lands 720a and 7201] near its opposite ends isreciprocably mounted within the housing. The valve 720 is urged to theleft into engagement with a stop member 624 by a spring 722 retainedbetween the right end of the valve and a fixed spring retaining element726.

When the manual selector valve U is positioned in any of its fivepositions except R reverse, the selector valve ,port 674 is closed and,therefore, fluid pressure cannot flow to the left side of the reverseshuttle valve 720 through conduit 678a, as a result spring 722 normallymaintains the valve 720 in its left hand positions, and

. gallery pressure from conduit 676a is permitted to flow between lands720a and 7201) into conduit 716, and thence to the upper (release) sideof the reverse brake piston 679. Thus, the reverse brake F is heldpositively in its inoperative position when any of the forward drivingranges are engaged.

When pressure is admitted to the left end of housing 710 through conduit678a, valve 720 is moved to the right so that land 720a covers port 718and land 72% uncovers radial vent port 728 in the housing. Gallerypressure then flows through manual selector valve U to conduits 678 and67819 to the under (operative) side of the reverse brake piston 679,engaging the reverse brake F. The fluid pressure on the upper side ofthe piston is vented through line 716 and vent port 728.

The operationof the above described automatic control system is similarto that described in the above referred copending McFarland, Lucia andDe Lorean application No. 498,404, dated March 31, 1955.

it will be apparent that other forms of the invention may be employedwithout departing from the spiritiof the invention, and it is to beunderstood that the following claims are not to be considered as limitedsolely to the details of construction and arrangement of partsillustrated and described in the specification.

What is claimed is:

1. In a transmission control system for a transmission adapted for usewith an accelerator controlled engine including a transmission outputshaft, hydraulic operated clutch to engage the high range drive,hydraulic operated brake means to engage and disengage the low range"drive, a fluid pressure reservoir, conduit means connecting with thereservoir and the high range engaging means and the rake means todisengage the low range drive, fluid conveying means connecting with thereservoir and the brake means to engage the low range drive, and controlmeans responsive to the rotation of the output shaft and to the movementof the accelerator pedal towards its speed increasing position foropening and closing the conduit means and the fluid conveying means, aregulating system comprising a regulator valve connecting with theconduit means for momentarily retarding the fluid pressure flow to thehigh range clutch means when the conduit means is opened by said controlmeans, means connecting with the conduit means for retarding the fluidpressure flow to the low range disengaging brake means when the conduitmeans is opened by said control means, and valve means connecting withthe conduit means on opposite sides of said retarding means which isoperatively responsive to the movement of the accelerator pedal forbypassing the retardingmeans when the accelerator pedal is moved apredetermined distance towards its maximum speed increasing position.

2. A regulating system as described in claim 1 wherein said regulatingvalve isvadapted to rapidly vent fluid pressure delivered to the highrange engaging means when the brake means engages the low rangedrive.

3.. A system as described in claim 1 wherein. said valve means includesa second regulator valve connecting with the conduit means on oppositesides of the pressure flow retarding means, said second regulator valvebeing movable in one direction to admit fluid pressure tothe low rangedisengaging brake means and thereby bypassing the retarding means, .andsaid second regulator valve being closed when moved in the oppositedirection, spring means to move said regulator valve in said oppositedirection and a control valve connecting with the reservoir which isoperatively responsive to the movement of the accelerator pedal fordelivering fluid pressure substantially proportional .to the speedincreasing position of the accelerator pedal to said second regulatorvalve to move the latter in said one direction.

4. In a transmission control system for a transmission adapted for usewith an accelerator pedal controlled engine including a transmissionoutput shaft, hydraulic operated means to engagethe high range ,drive,hydraulic operated brakemeans to engage and disengage the low rangedrive, a fluid pressure reservoir, conduit means connecting with thereservoir and the high range clutch means, fluid conveying meansconnecting with the reservoir and thebrake means to engage the 'lowrange drive, and control means responsive to the rotation of the outputshaft and to the movement of the accelerator pedal towards its speedincreasing position for opening and closing the conduit means and thefluid conveying means, a regulating system comprising a regulatorvalveconnecting with the conduit means for admitting an increasing, thensteady and thereafter an increasing fluid pressure flow to the highrange engaging means when said conduit means is opened by said controlmeans; a branch conduit connecting with the conduit means between theregulator valve and the reservoir, and with the brake means to disengagethe low range drive; means connecting with the branch conduit forretarding the fluid pressure flow to the low range disengaging means, avalve connecting with the branch conduit on opposite sides of thepressure flow retarding means which is opened when moved in onedirection and closed when moved in the opposite direction, spring meansto move the valve in said opposite direction and a control valveconnecting with the reservoir which is operatively responsive to themovement of the accelerator pedal for delivering fluid pressuresubstantially proportional to the speed increasing position of theaccelerator pedal to said valve to move the latter in said onedirection.

5. A system as described in claim 4 including a limit valve connected inseries between the control valve and said valve to limit the pressuredelivered to the latter by a predetermined value, and wherein the forceof said spring means is such that the pressure delivered by said controlvalve will move said valve in said one direction when the pressureexceeds approximately 10% of its maximum value.

6. A regulating system as described in claim 4 wherein the regulatorvalve is adapted to rapidly vent fluid pressure delivered to the highrange clutch means when the low range brake is engaged.

7. In a control system for a transmission adapted for use with anaccelerator pedal controlled engine, including low and high drivingranges, hydraulic clutch means to engage the high range drive, a fluidpressure reservoir, conduit means connecting the reservoir and clutchmeans and control means to admit fluid pressure from said reservoir tosaid conduit means, a regulator valve comprising a valve housing havingclosed ends and inlet and outlet ports near one end thereof connectingin series with said conduit means, and a return port disposed betweensaid outlet port and said one end of the housing, a valve memberreciprocably mounted within said housing near said one end thereof, saidvalve member being adapted to deliver full pressure flow to the outletport when moved in one direction and to deliver a reduced pressure flowto the outlet port when moved in the opposite direction, a fluidconveying means connecting the outlet port and the return port todeliver fluid pressure therethrough to move said valve member in saidopposite direction, a piston means reciprocably mounted within thehousing near its opposite end, resilient means to urge said piston meansinto engagement with said valve member, thereby moving the valve memberin said one direction, branch conduit means connecting with said conduitmeans and said housing to deliver fluid pressure therethrough to movesaid piston toward said opposite end of the housing and to move saidvalve member in one direction, and means connecting with said branchconduit to retard the fluid pressure flow to the housing, whereby, whenpressure is admitted to said conduit means by said control means, saidresilient means first acts to move said valve member in said onedirection, and thereafter the branch conduit pressure moves the valvemember in said one direction thereby increasing the fluid pressure flowthrough the outlet port of the regulator valve.

8. In a control system for a transmission adapted for use with anaccelerator pedal controlled engine, including low and high drivingranges, hydraulic clutch means to engage the high range drive, a fluidpressure reservoir,

conduit means connecting the reservoir and clutch means, and controlmeans to admit fluid pressure from the reser voir to the conduit means,a regulator valve comprising a valve housing having closed ends andinlet and outlet ports near one end thereof connecting in series withsaid conduit means, and a return port disposed between said outlet portand said one end of the housing, a valve member reciprocably mountedwithin said housing near said one end thereof, said valve member havingone land formed near an end thereof nearest said one end of the housing,and another land formed about its opposite end; said valve member landsbeing disposed so that when said valve member is moved toward said oneend of the housing full pressure flows between the lands to the outletport, and when said valve member is moved toward the opposite end of thehousing said one land partially covers the outlet port to reduce thepressure flow therethrough, fluid conveying means connecting the outletport and the return port to deliver fluid pressure to move said valvemember toward the opposite end of the housing, a piston memberreciprocable within the housing near its opposite end, spring means tourge said piston member into engagement with said valve member to movesaid valve member toward said one end of the housing, an inlet port insaid housing communicating with the interior thereof between said valvemember and said piston member, a branch conduit connecting said conduitmeans and said last mentioned inlet port to deliver fluid pressure tomove said piston member toward the opposite end of the housing and tomove said valve member toward said one end of the housing, and meansconnecting with said branch conduit to retard the fluid pressure flowtherethrough to said last mentioned inlet port, whereby, when pressureis admitted to said conduit means by said control means, said resilientmeans first acts to move said valve member toward said one end of thehousing, and thereafter the branch conduit pressure exerts a greaterforce to move the valve member toward said one end of the housing,thereby increasing the fluid pressure flow through the outlet port ofthe regulator valve.

9. A regulator valve as described in claim 8 wherein said valve memberhas an axial bore extending partially therethrough from its end nearestsaid one end of the housing, a radial bore near the middle of said valvemember communicating with said axial bore, a vent port communicatingwith the interior of the housing near the middle thereof, said radialbore being moved into alignment with said vent port when said valvemember is moved its maximum distance towards said opposite end of thehousing, whereby fluid pressure from the high range clutch meansdelivered through the return port may flow through the vent port whenthe outlet port pressure exceeds a predetermined value and when nopressure is admitted to the conduit means by said control means.

10. A regulator valve as described in claim 9 wherein the fluid pressuredelivered to the return port by said fluid conveying means first reactsagainst a side of said one land to move the valve member slowly towardthe opposite end of the housing, and thereafter the return port pressurereacts against said end of the valve member nearest said one land andsaid one end of the housing, a substantially greater force acts to movethe valve member toward the opposite end of the housing.

No references cited.

